Received signal quality determination

ABSTRACT

A method of generating a received signal quality signal in a communication system, the method comprising: receiving a signal from a physical channel, extracting a transport channel format combination indicator from the received signal, processing one or more transport channel signals, contained in the received signal, in accordance with the extracted transport channel format combination indicator, said processing including at least channel decoding, and generating a received signal quality signal in dependence on the quality of the or each transport channel signal prior to channel decoding.

FIELD OF THE INVENTION

The present invention relates to the determination of received signalquality in a radio communication system.

BACKGROUND TO THE INVENTION

In a radio communication network, such as a mobile phone network, mobilestations monitor the quality of received signals and report the receivedsignal quality back to a base station, typically in a control channel.

It has been proposed that a mobile station report received signalquality in a slow associated control channel (SACCH) using a three bitcode. The signal quality is determined as the bit error rate (BER) ofthe received signal before channel decoding and is averaged over oneSACCH multiframe, for example 480 ms.

The BER is only used if the a block is correctly received, i.e. itpasses a CRC (cyclic redundancy code) check. If a block is not correctlyreceived, a default notional BER of, for example 50%, is assumed.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda method of generating a received signal quality signal in acommunication system, the method comprising:

-   -   receiving a signal from a physical channel;    -   extracting a transport channel format combination indicator from        the received signal;    -   processing one or more transport channel signals, contained in        the received signal, in accordance with the extracted transport        channel format combination indicator; said processing including        at least channel decoding; and    -   generating a received signal quality signal in dependence on the        quality of the or each transport channel signal prior to channel        decoding.

According to the first aspect of the present invention, there is alsoprovided a communication device comprising:

-   -   a receiver for receiving a signal from a physical channel;    -   processing means configured for:        -   extracting a transport channel format combination indicator            from the received signal;        -   processing one or more transport channel signals, contained            in the received signal, in accordance with the extracted            transport channel format combination indicator; said            processing including at least channel decoding; and        -   generating a received signal quality signal in dependence on            the quality of the or each transport channel signal prior to            channel decoding.

The or each transport channel signal may comprise a sequence of datablocks. The quality of the or each transport channel signal may berepresented by a block bit error rate determined prior to channeldecoding. The determined bit error rate of a transport channel signalmay be averaged over period comprising a plurality of data blocks. Inthe case of there being a plurality of transport channel signals, thebit error rates of each transport channel signal may be averaged overthe same period. An average bit error rate may be calculated across thetransport channel signals with the averaging being weighted independence on the transport formats used for said transport signals.

The received signal quality signal may be transmitted in a controlchannel.

According to a second aspect of the present invention, there is provideda method of generating a received signal quality signal in acommunication system, the method comprising:

-   -   receiving a signal from a physical channel, the signal        comprising one or more transport channels;    -   extracting a transport channel format combination indicator from        the received signal and determining the bit error rate        therefore, and    -   generating a received signal quality signal in dependence on the        bit error rate of the extracted transport channel format        combination indicator.

According to the second aspect of the present invention, there is alsoprovided a communication device comprising:

-   -   a receiver for receiving a signal from a physical channel, the        signal comprising one or more transport channels; and    -   processing means configured for:        -   extracting a transport channel format combination indicator            from a received signal and determining the bit error rate            therefore; and        -   generating a received signal quality signal in dependence on            the bit error rate of the extracted transport channel format            combination indicator.

The determined bit error rates of a plurality of transport channelformat combination indicator instances may be averaged.

The received signal quality signal may be transmitted in a controlchannel.

According to a third aspect of the present invention, there is provideda method of generating a received signal quality signal in acommunication system, the method comprising:

-   -   receiving a signal from a physical channel, the signal        comprising a plurality of bursts each including a training        sequence; and    -   generating a received signal quality signal in dependence on the        bit error rate of the training sequence of a received burst.

According to the third aspect of the present invention, there is alsoprovided a communication device comprising:

-   -   a receiver for receiving a signal from a physical channel, the        signal comprising a plurality of bursts each including a        training sequence; and    -   processing means configured for generating a received signal        quality signal in dependence on the bit error rate of the        training sequence of a received burst.

The determined bit error rates of the training sequences of a pluralityof bursts may be averaged.

The bit error rate of a training sequence may be produced by comparing areceived training sequence with a reference training sequence.

The received signal quality signal may be transmitted in a controlchannel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a mobile communication system according to the presentinvention;

FIG. 2 is a block diagram of a mobile station;

FIG. 3 is a block diagram of a base transceiver station;

FIG. 4 illustrates the frame structure;

FIG. 5 illustrates a packet data channel;

FIG. 6 illustrates the sharing of a radio channel between two half-ratepacket channels;

FIG. 7 illustrates the lower levels of a protocol stack;

FIG. 8 is a block diagram illustrating the processing of the transportchannels of a received physical layer signal;

FIG. 9 is a block diagram illustrating received signal qualitydetermination;

FIG. 10 is a flowchart of a first part of a received signal qualitydetermination process;

FIG. 11 is a flowchart of a second part of a received signal qualitydetermination process;

FIG. 12 is a block diagram illustrating another approach to signalquality determination;

FIG. 13 is a flowchart illustrating another received signal qualitydetermination process;

FIG. 14 is a block diagram illustrating yet another approach to signalquality determination; and

FIG. 15 is a flowchart illustrating yet another received signal qualitydetermination process.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings.

Referring to FIG. 1, a mobile phone network 1 comprises a plurality ofswitching centres including first and second switching centres 2 a, 2 b.The first switching centre 2 a is connected to a plurality of basestation controllers including first and second base station controllers3 a, 3 b. The second switching centre 2 b is similarly corrected to aplurality of base station controllers (not shown).

The first base station controller 3 a is connected to and controls abase transceiver station 4 and a plurality of other base transceiverstations. The second base station controller 3 b is similarly connectedto and controls a plurality of base transceiver stations (not shown).

In the present example, each base transceiver station services arespective cell. Thus, the base transceiver station 4 services a cell 5.However, a plurality of cells may be serviced by one base transceiverstation by means of directional antennas. A plurality or mobile stations6 a, 6 b are located in the cell 5. It will be appreciated what thenumber and identities of mobile stations in any given cell will varywith time.

The mobile phone network 1 is connected to a public switched telephonenetwork 7 by a gateway switching centre 8.

A packet service aspect of the network includes a plurality of packetservice support nodes (one shown) 9 which are connected to respectivepluralities of base station controllers 3 a, 3 b. At least one packetservice support gateway node 10 connects the or each packet servicesupport node 10 to the Internet 11.

The switching centres 3 a, 3 b and the packet service support nodes 9have access to a home location register 12.

Communication between the mobile stations 6 a, 6 b and the basetransceiver station 4 employs a time-division multiple access (TDMA)scheme.

Referring to FIG. 2, the first mobile station 6 a comprises an antenna101, an rf subsystem 102, a baseband DSP (digital signal processing)subsystem 103; an analogue audio subsystem 104, a loudspeaker 105, amicrophone 106, a controller 107, a liquid crystal display 108, a keypad109, memory 110, a battery 111 and a power supply circuit 112.

The rf subsystem 102 contains if and rf circuits of the mobiletelephone's transmitted and receiver and a frequency synthesizer fortuning the mobile station's transmitter and receiver. The antenna 101 iscoupled to the rf subsystem 102 for the reception and transmission ofradio waves.

The baseband DSP subsystem 103 is coupled to the rf subsystem 102 toreceive baseband signals therefrom and for sending baseband modulationsignals thereto. The baseband DSP subsystems 103 includes codecfunctions which are well-known in the art.

The analogue audio subsystem 104 is coupled to the baseband DSPsubsystem 103 and receives demodulated audio therefrom. The analogueaudio subsystem 104 amplifies the demodulated audio and applies it tothe loudspeaker 105. Acoustic signals, detected by the microphone 106,are pre-amplified by the analogue audio subsystem 104 and sent to thebaseband DSP subsystem 4 for coding.

The controller 107 controls the operation of the mobile telephone. It iscoupled to the rf subsystem 102 for supplying tuning instructions to thefrequency synthesizer and to the baseband DSP subsystem 103 forsupplying control data and management data for transmission. Thecontroller 107 operates according to a program stored in the memory 110.The memory 110 is shown separately from the controller 107. However, itmay be integrated with the controller 107.

The display device 108 is connected to the controller 107 for receivingcontrol data and the keypad 109 is connected to the controller 107 forsupplying user input data signals thereto.

The battery 111 is connected to the power supply circuit 112 whichprovides regulated power at the various voltages used by the componentsof the mobile telephone.

The controller 107 is programmed to control the mobile station forspeech and data communication and with application programs, e.g. a WAPbrowser, which make use of the mobile station's data communicationcapabilities.

The second mobile station 6 b is similarly configured.

Referring to FIG. 3, greatly simplified, the base transceiver station 4comprises an antenna 201, an rf subsystem 202, a baseband DSP (digitalsignal processing) subsystem 203, a base station controller interface204 and a controller 207.

The rf subsystem 202 contains the if and rf circuits of the basetransceiver station's transmitter and receiver and a frequencysynthesizer for tuning the base transceiver station's transmitter andreceiver. The antenna 201 is coupled to the rf subsystem 202 for thereception and transmission of radio waves.

The baseband DSP subsystem 203 is coupled to the rf subsystem 202 toreceive baseband signals therefrom and for sending baseband modulationsignals thereto. The baseband DSP subsystems 203 includes codecfunctions which are well-known in the art.

The base station controller interface 204 interfaces the basetransceiver station 4 to its controlling base station controller 3 a.

The controller 207 controls the operation of the base transceiverstation 4. It is coupled to the rf subsystem 202 for supplying tuninginstructions to the frequency synthesizer and to the baseband DSPsubsystem for supplying control data and management data fortransmission. The controller 207 operates according to a program storedin the memory 210.

Referring to FIG. 4, each TDMA frame, used for communication between themobile stations 6 a, 6 b and the base transceiver stations 4, compriseseight 0.577 ms time slots. A “26 multiframe” comprises 26 frames and a“51 multiframe” comprises 51 frames. Fifty one a “26 multiframes” ortwenty six “51 multiframes” make up one superframe. Finally, ahyperframe comprises 2048 superframes.

The data format within the time slots varies according to the functionof a time slot. A normal burst, i.e. time slot, comprises three tailbits, followed by 58 encrypted data bits, a 26-bit training sequence,another sequence of 58 encrypted data bits and a further three tailbits. A guard period of eight and a quarter bit durations is provided atthe end of the burst. A frequency correction burst has the same tailbits and guard period. However, its payload comprises a fixed 142 bitsequence. A synchronization burst is similar to the normal burst exceptthat the encrypted data is reduced to two clocks of 39 bits and thetraining sequence is replaced by a 64-bit synchronization sequence.Finally, an access burst comprises eight initial tail bits, followed bya 41-bit synchronization sequence, 36 bits of encrypted data and threemore tail bits. In this case, the guard period is 68.25 bits long.

When used for circuit-switched speech traffic, the channelisation schemeis as employed in GSM.

Referring to FIG. 5, full rate packet switched channels make use of 124-slot radio packets spread over a “51 multiframe”. Idle slots followthe third, sixth, ninth and twelfth radio packet.

Referring to FIG. 6, for half rate, packet switched channels, bothdedicated and shared, slots are allocated alternately to twosub-channels.

The baseband DSP subsystems 103, 203 and controllers 107, 207 of themobile stations 6 a, 6 b and the base transceiver stations 4 areconfigured to implement two protocol stacks. The first protocol stack isfor circuit switched traffic and is substantially the same as employedin conventional GSM systems. The second protocol stack is for packetswitched traffic.

Referring to FIG. 7, the layers relevant to the radio link between amobile station 6 a, 6 b and a base station controller 4 are the radiolink control layer 401, the medium access control layer 402 and thephysical layer 403.

The radio link control layer 401 has two modes: transparent andnon-transparent. In transparent mode, data is merely passed up or downthrough the radio link control layer without modification.

In non-transparent mode, the radio link control layer 401 provides linkadaptation and constructs data blocks from data units received fromhigher levels by segmenting or concatenating the data units as necessaryand performs the reciprocal process for data being passed up the stack.It is also responsible for detecting lost data blocks or reordering datablock for upward transfer of their contents, depending on whetheracknowledged mode is being used. This layer may also provide backwarderror correction in acknowledged mode.

The medium access control layer 402 is responsible for allocating datablocks from the radio link control layer 401 to appropriate transportchannels and passing received radio packets from transport channels tothe radio link control layer 403.

The physical layer 403 is responsible to creating transmitted radiosignals from the data passing through the transport channels and passingreceived data up through the correct transport channel to the mediumaccess control layer 402.

Referring to FIG. 8, data produced for applications 404 a, 404 b, 404 cpropagates up the protocol stack from the medium access control layer402. The data from the applications 404 a, 404 b, 404 c can belong toany of a plurality of classes for which different qualities of serviceare required. Data belonging to a plurality of classes may be requiredby a single application. The medium access control layer 402 directsdata to the applications 404 a, 404 b, 404 c from different transportchannels 405, 406, 407 according to class to which it belongs.

Each receive transport channel 405, 406, 407 can be configured toprocess received signals according to a plurality of processing schemes405 a, 405 b, 405 c, 406 a, 406 b, 406 c, 407 a, 407 b, 407 c. Theconfiguration of the transport channels 405, 406, 407 is establishedduring call setup on the basis of the capabilities of the mobile station6 a, 6 b and the network and the nature of the application orapplications 404 a, 404 b, 404 c being run.

The processing schemes 405 a, 405 b, 405 c, 406 a, 406 b, 406 c, 407 a,407 b, 407 c are unique combinations of cyclic redundancy check 405 a,406 a, 407 a, channel decoding 405 b, 406 b, 407 b and rate matching 405c, 406 c, 407 c. These unique processing schemes are the reciprocals oftransmitter processing schemes which define different “transportformats”. An interleaving scheme may be selected for each transportchannel 405, 406, 407 and require corresponding de-interleaving 405 d,406 d, 407 d. Thus, different transport channels may use differentinterleaving schemes and, in alternative embodiments, differentinterleaving schemes may be used at different times by the sametransport channel.

The combined data rate produced for the transport channels 405, 406, 407must not exceed that of physical channel or channels allocated to themobile station 6 a, 6 b. This places a limit on the transport formatcombinations that can be permitted For instance, if there are threetransport formats TF1, TF2, TF3 for each transport channel, thefollowing combinations might be valid: —

-   -   TF1 TF1 TF2    -   TF1 TF3 TF3        but not    -   TF1 TF2 TF2    -   TF1 TF1 TF3

The received signal is de-interleaved 411 and then demultiplexed by ademultiplexing process 410, which outputs transport channel signals torespective transport channel de-interleaving processes 405 d, 406 d, 407d.

A transport format combination indicator is spread across one radiopacket with portions placed in fixed positions in each burst, on eitherside of the training symbols (FIG. 9) in this example. The completetransport format combination indicator therefore occurs at fixedintervals, i.e. the block length 20 ms. This makes it possible to ensuretransport format combination indicator detection when differentinterleaving types are used e.g. 8 burst diagonal and 4 burstrectangular interleaving. Since the transport format combinationindicator is not subject to variable interleaving, it can be readilylocated by the receiving station and used to control processing of thereceived data.

The transport format combination indicator is extracted from thereceived data stream by a transport format combination indicatorextraction process 414 after the deinterleaving process 411.

The transport format combination indicator from the transport formatcombination indicator extraction process 414 is decoded by a decodingprocess 413. The decoded transport format combination indicator is thenprocessed by a transport format combination detecting process 412 whichprovides information on the current transport format combination to themedium access control layer 402. This information is then used in themedium access control layer 402 to select the appropriate decoding andde-interleaving process for the transport formats used in the receivedsignal.

FIG. 9 illustrates received signal quality determination in the casewhere the received physical layer signal carries a data streamcomprising three transport channels using respective formats. Of course,the data stream may comprise more or fewer transport channels and thesame transport format may be used by more than one of the transportchannels.

Referring to FIG. 9, first, second and third transport channel qualitydeterminers 501, 502, 503 receive the cyclic redundancy check resultsfrom respective cyclic redundancy check processes 405 a, 406 a, 407 aand a bit error rate estimate from respective channel decoding processes405 b, 406 b, 407 b.

The operation of the first transport channel quality determiner 501 willnow be described with reference to FIG. 10.

Referring to FIG. 10, at the start of a SACCH multiframe period (alsoknown as the SACCH reporting period), the CRC result for a firsttransport block is received from the first cyclic redundancy checkprocess 405 a (step s1). If the result is determined to be true, i.e.the CRC is correct, (step s2), the BER for the first transport block isobtained from the first channel decoder 405 b (step s3) and stored (steps4). A block counter is then incremented (step s5). It is thendetermined whether the current SACCH multiframe period has come to anend (step s6).

If the current SACCH multiframe period has not come to an end (step s6),the program flow returns to step s1 where the CRC for the next block isobtained.

If, at step s2, it is determined that the cyclic redundancy check resultis determined to be false, steps s3 to s5 are skipped.

When all of the blocks of the current the current SACCH multiframeperiod have been processed (step s6), the BER is averaged over a periodcorresponding to the product of the block period and the number ofcorrectly received transport blocks, i.e. the value accumulated by thestep s5.

The second and third transport channel quality determiners 502, 503operate in the same way as the first transport channel qualitydeterminers 501 except that the cyclic redundancy check result and theBE R estimates are obtained from the corresponding cyclic redundancycheck process 406 a, 407 a and channel decoders 406 b, 407 b.

The transport channel quality determiners 501, 502, 503 output theiraverage BERs and transport block counts to a physical channel qualitydeterminer 504.

The operation of the physical channel quality determiner 504 will now bedescribed with reference to FIG. 11.

Referring to FIG. 11, the physical channel quality determiner 504obtains the TFCI applicable to the most recent transport channel qualitydeterminations (step s11) and then receives the transport block countsfrom the transport channel quality determiners 501, 502, 503 (step s12).

The TFCI information determines what percentage of each radio packet isused by each transport channel. This information is used to convert thetransport block counts into the percentage of the data in thetransmitted data stream that was correctly received in one SACCHmultiframe, according to:

$P = {\sum\limits_{c = 1}^{n}\frac{{b(c)} \cdot {p(c)}}{b_{T}(c)}}$

where c is the transport channel number, n is the number of transportchannels, b is the number of correctly received bits in the transportblock, b_(T) is the number of bits in the transport block in thetransmitted signal and p is the percentage of the data stream used by aparticular transport channel.

If the result P is greater than or equal to 50%, the BERs are obtainedfrom the transport channel quality determiners 501, 502, 503 (step s15).The BERs are then averaged (step s16). In the present embodiment, theBERs are averaged in accordance with the following:

$B = \frac{\sum\limits_{c = 1}^{n}{{b(c)} \cdot {p(c)}}}{\sum\limits_{c = 1}^{n}{p(c)}}$

where B is the average BER.

If, however, the percentage of the data in the transmitted data streamthat was incorrectly received is greater than 50% (step s14), theaverage bit error rate B is set arbitrarily to 50%.

The average bit error rate B is then quantized and encoded into 3 bitswhich are made available for transmission to a base transceiver station4 by the mobile station 6 a in the SACCH as a received signal qualityreport.

It will be appreciated that the formulae given above are examples of theeffect required and that the value ranges and scaling factors actualused may vary.

A second embodiment of the present invention will now be described.

A mobile station is as described above with the exception of thegeneration of the received signal quality report. In this embodiment,the report is based on the quality of the TFCI signal.

Referring to FIG. 12, TFCI BERs are fed from the TFCI decoder 413 (FIG.8) to a received signal quality determiner 601. The received signalquality determiner 601 generates a received signal quality signal independence on the TFCI BERs from the TFCI decoder 413 and outputs it fortransmission in the SACCH.

Referring to FIG. 13, the received signal quality determiner 601 obtainsa first TFCI BER for the first TFCI transmitted in a SACCH multiframeperiod (step s31) and stores it (step s32). Successive TFCI BERs arethen obtained (step s31) and stored (step s32) until the BER for thelast TCFI of the current SACCH multiframe period ends (step s33).

When the last BER has been obtained and stored, the stored BERs areaveraged (step s34) and then the average quantized and encoded (steps35) and output (step s36) for transmission to a base transceiverstation 4 by the mobile station 6 a in the SACCH as a received signalquality report.

A third embodiment of the present invention will now be described.

A mobile station is as described above with the exception of thegeneration of the received signal quality report. In this embodiment,the report is based on the quality of the received training sequences.

As shown in FIG. 4, each burst comprises a training sequence sandwichedbetween two blocks of data bits. The training sequences arepredetermined.

Referring to Referring to FIG. 14, received training sequences are fedto a received signal quality determiner 701. The received signal qualitydeterminer 701 generates a received signal quality signal in dependenceon the received training sequences and outputs it for transmission inthe SACCH.

Referring to FIG. 12, TFCI BERs are fed from the TFCI decoder 413 (FIG.8) to a received signal quality determiner 601. The received signalquality determiner 601 generates a received signal quality signal independence on the TFCI BERs from the TFCI decoder 413 and outputs it fortransmission in the SACCH.

Referring to FIG. 15, the received signal quality determiner 701 obtainsa first training sequence in a SACCH multiframe period (step s41) andcompares it with a reference copy (step s42). The number of differencesbetween the received training sequence and the reference is added to arecord of the errors for the current SACCH multiframe period (step 43).The errors in successive training sequences are then obtained (step s42)and added to the error record (step s43) until the training sequence ofthe last burst in the current SACCH multiframe period has been processed(step s44).

When the last training sequence has been processed, the accumulatederror count is quantized (step s45) and output (step s46) fortransmission to a base transceiver station 4 by the mobile station 6 ain the SACCH as a received signal quality report.

The three embodiments described above may be combined to produceadditional embodiments. For instance, bit error rates obtained by two orthree techniques may be averaged to produce a bit error rate that isthen quantized, encoded and transmitted to a base transceiver station 4by the mobile station 6 a in the SACCH as a received signal qualityreport.

It is to be understood that the foregoing embodiments are merelyexamples and that many modifications are possible without departing fromthe spirit and scope of the appended claims.

1.-20. (canceled)
 21. A method of generating a received signal qualitysignal in a communication system, the method comprising: receiving asignal from a physical channel, the signal comprising a plurality ofbursts each including a training sequence; and generating a receivedsignal quality signal in dependence on the bit error rate of thetraining sequence of a received burst.
 22. The method according to claim21, wherein the determined bit error rates of the training sequences ofa plurality of bursts are averaged.
 23. The method according to claim21, wherein the bit error rate of a training sequence is produced bycomparing a received training sequence with a reference trainingsequence.
 24. The method according to claim 21, further includingtransmitting the received signal quality signal in a control channel.25. A communication device comprising: a receiver to receive a signalfrom a physical channel, the signal comprising a plurality of bursts,each including a training sequence; and processing means configured togenerate a received signal quality signal in dependence on the bit errorrate of the training sequence of a received burst.
 26. The deviceaccording to claim 25, wherein the processing means is configured toaverage the determined bit error rates of the training sequences of aplurality of bursts.
 27. The device according to claim 25, wherein theprocessing means is configured to produce the bit error rate of atraining sequence by comparing a received training sequence with areference training sequence.
 28. The device according to claim 25,further including a transmitter, wherein the processing means isconfigured to cause the transmitter to transmit the received signalquality signal in a control channel of a communication network.
 29. Aprocessor-readable medium containing processor-executable instructionsthat, when executed by a processor, cause the processor to implement amethod of generating a received signal quality signal in a communicationsystem, the method comprising: receiving a signal from a physicalchannel, the signal comprising a plurality of bursts each including atraining sequence; and generating a received signal quality signal independence on the bit error rate of the training sequence of a receivedburst.
 30. The medium according to claim 29, wherein the determined biterror rates of the training sequences of a plurality of bursts areaveraged.
 31. The medium according to claim 29, wherein the bit errorrate of a training sequence is produced by comparing a received trainingsequence with a reference training sequence.
 32. The medium according toclaim 29, wherein the method further includes transmitting the receivedsignal quality signal in a control channel.